Optical signals may be made to carry information by modulating a light source, often a laser source, to change various properties of the light, such as its amplitude, phase, frequency, wavelength, etc. The light waves may be in the visible spectral band, the infrared spectral band, or another region of the electromagnetic spectrum. In some cases, an underlying signal, such as a radio frequency signal, may be modulated via amplitude, phase, or frequency modulation, or any combination thereof, and the light source may be modulated by the underlying signal. Optical receivers receive the light waves and measure properties or variations of the light wave, such as the amplitude, phase transitions, and the like, from which the underlying signal and the information may be recovered.
Various light signals may include phase modulation, as well as amplitude or other modulation, that may encode information such as transmitted communication data, or may include other information such as information about the source of the optical signal, information about the optical channel through which the optical signal traveled, information about interaction of the optical signal with an object, and/or information about one or more objects with which the optical signal interacted. Receivers capable of demodulating phase modulation can be highly complex, requiring precision optics, local oscillators, gratings (such as Fiber Bragg Gratings), and/or delay line interferometers (DLI), etc.